The downward pointing triangle is a very ancient symbol of the Primal
Female, the Origin of All Things, pubic triangle of the Great Goddess.
A Yantra is a geometrical manifestation of a deity's energy (Mantra is
a sound manifestation of same). Kali's Yantra has five nested triangles,
and flower petals sometimes within or around.
It is a beautiful image of feminine strength, power,
and clarity. [See a colorful array by
searching for "Kali Yantra" in Google Images]